Method of producing aluminum planographic printing plates

ABSTRACT

A PROCESS OF PRODUCING ALUMINUM CONTAINING SUPPORTS, WHICH COMPRISES ETCHING A GRAINED ALUMINUM SURFACE WITH A BASIC OR ACIDIC ETCHING SOLUTION WITHIN THE RANGE OF 0.5 TO 30 G./M.2 AND THEN SUBJECTING THE ETCHED SURFACE TO ANODIC OXIDATION.

United States Patent Oflice 3,834,998 METHOD OF PRODUCING ALUMINUM PLANOGRAPHIC PRINTING PLATES Masaru Watanabe and Azusa Ohashi, Odawara-shi, Kanagawa, Japan, assignors to Fuji Photo Film Co., Ltd., Minami-ashigara-shi, Kanagawa, Japan No Drawing. Filed Oct. 18, 1972, Ser. No. 298,751 Claims priority, application Japan, Oct. 21, 1971, 46/813,482 Int. Cl. C23b 9/02 US. Cl. 204-33 16 Claims ABSTRACT OF THE DISCLOSURE A process of producing aluminum containing supports, which comprises etching a grained aluminum surface with a basic or acidic etching solution within the range of 0.5 to 30 g./m. and then subjecting the etched surface to anodic oxidation.

BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a method of producing aluminum supports. As used in this specification, aluminum includes both aluminum and aluminum alloys such as those comprising greater than 95% by Weight of aluminum and less than 5% by weight of other metals, for example, manganese, copper, zinc, titanium, iron, magnesium, chromium and the like. Suitable examples of aluminum alloys which can be used in the present invention are AA 1100, AA 3003, etc. (The symbol AA is an abbreviation for American Aluminum Association.)

Description of the Prior Art In general, planographic printing is a method wherein reproduction is carried out by forming a water-Wettable or hydrophilic non-image area and a water-repellent and oil-miscible image area on a plate, adhering water to the non-image area and a printing ink to the image area utilizing the repellency of the water for the printing ink and then transferring the ink onto the desired copy.

In such methods, a thin metal plate such as an aluminum or zinc plate is used as the plate support and nonimage forming material, while a film of light-sensitive organic compound such as a bi-chromate colloid, a diazonium compound or a light-sensitive resin is used as the image forming material. Usually an aluminum or zinc plate is surface-treated and coated with a light-sensitive film and then processed so that only the image area retains a film by adhesion to the metal plate. This is usually accomplished using a photographic method (exposuredevelopment) Various surface treatment methods have been proposed for the purpose of raising and strengthening the adhesive force between the image yielding film and the aluminum support as well as the adaptability of a non-image area, e.g., the hydrophilic and water-retaining properties.

The most commonly employed method consists in providing a fine roughness on the metal surface by a surface polishing technique such as polishing using small steel or porcelain balls with a polishing agent peculiar to the printing field, sandblasting, liquid honing or brushing. As methods for raising image adhesion and hydrophilic properties by chemical film forming, immersion treatments such as using sodium silicate, fluozirconate, polycarbonate and polyphosphate have been employed.

A recent development in the art has been to subject an aluminum plate to anodic oxidation. As a method for the anodic oxidation of aluminum, electrolysis through direct current in aqueous sulfuric acid is generally employed.

7 3,834,998 Patented Sept. 10, 1974 It has also been reported that an anodically oxidized plate wherein phosphoric acid was used in the anodic oxidation has been used as a printing plate.

As a result of our studies, it has been made apparent that an aluminum plate which is grained and subjected to anodic oxidation through direct current electrolysis in sulfuric acid has excellent properties as a printing plate. That is to say, in comparison with a printing plate which has not been subjected to anodic oxidation, the former gives excellent results in printing with respect to abrasion resistance, printing durability, scratch resistance, hydrophilic property and water retaining property (water retaining property of a non-image area).

Considering all the properties thereof as a printing plate, however, some faults are presented by such a plate. Firstly, when a grained aluminum plate is subjected to electrolysis, the plate surface tends to blacken. It was thought this phenomenon was due to the residue of polishing powder used for graining, but this discoloration takes place with any of the foregoing polishing methods and is unavoidable even With profuse Washing after polishing. Furthermore, this phenomenon is very increased by any non-uniformity or variation in the polished state of the plate. This blackening phenomenon results not only in a marked deterioration of the appearance of the printing plate but also lowers the sensitivity of a light-sensitive layer coated thereon during printing plate manufacture. Moreover, even after development, discrimination of an image area is very difficult and the operations of retouching and image elimination, essential for plate making, are hindered. For the same reason, the workers judgment regarding the control of the moisture and ink is also diflicult in the printing operation.

The second important problem with such prior art printing plates is that elimination of the light-sensitive layer on a non-image area (development) is diflicult. It is known that the adhesion of a film coated onto a grained surface is raised by previously subjecting it to anodic oxidation, but upon removing the film the coating ingredients remain on the grained surface to a greater extent than on a surface not subjected to anodic oxidation. In this respect, a printing plate using a support previously subjected to anodic oxidation is inferior to one using a support not subjected to anodic oxidation since a non-image area is liable to be spoiled during printing unless the developing operation is carefully carried out with a strong developer in a large amount.

SUMMARY OF THE INVENTION We, the inventors, have made efforts to solve these problems, which are important in the printing field, and have found that very good results are obtained by etching the grained surface, after graining but before anodic oxidation, with a basic or acidic treating solution capable of dissolving aluminum (aluminum etching solution) within a range of 0.5-30 g./m.

DETAILED DESCRIPTION OF THE INVENTION As the graining method of the invention, any generally used prior art polishing method can be used including methods involving using polishing powders such as alumina, Carbonundum, diamond and pumice powder, for example, ball polishing, sandblasting, liquid honing and brush polishing. The preferred degree of roughening is from about 0.2 to about 1.5 in terms of Ha value. Unevenness on the surface of aluminum plates should be regulated by so-called cut off. In the present invention, the preferred cut off value is 0.75 mm., which refers to cutting off unevenness greater than 0.75 mm.

The etching solution used in the present invention can be chosen from any basic or acidic aqueous solution capable of dissolving aluminum. In this case, however,

the etching solution should be one such that there is formed on an etched surface no film derived from the aluminum or the etching solution which is diflerent from aluminum. The acidic etching solution preferably has a pH value less than about 3, while the basic etching solution preferably has a pH value greater than 11. In either case, the concentration of the etching agent in the solution will usually range from about 3 to about 30% by weight. Needless to say, a pH and concentration above and below the recited preferred ranges can be used, though processing may be slower.

Preferred etching agents are basic materials such as sodium hydroxide, potassium hydroxide, trisodium phosphate, disodium phosphate, tripotassium phosphate and dipotassium phosphate, and acidic materials such as sulfuric acid, persulfuric acid and their salts. However, salts of a metal having a lower ionization potential than aluminum,

such as zinc, chromium, cobalt, nickel or copper, are not desirable because these salts tend to form unnecessary films.

These etching agents are preferably used at a temperature and concentration so that the rate of dissolution of aluminum is about 0.3 to about 40 g./m. per 1 minute of immersion time, the temperature usually ranging from about 25 to about 90 C. of course, the rate of dissolution may be varied outside this range without encountering inoperable results.

Etching is ordinarly carried out by immersing a grained aluminum plate in the above mentioned etching solution or by coating the aluminum plate with the etching solution. The etched plate is usually washed prior to anodic oxidation.

The anodic oxidation maybe carried out using any well known prior art aluminum etching system preferably in sulfuric acid, oxalic acid, phosphoric acid, chromic acid or mixed system thereof, most preferably in sulfuric acid. The concentration of electrolyte, current density during electrolysis and electrolysis time may be in accordance with prior art techniques, and there is no limitation on the apparatus which can be used.

In the case of using sulfuric acid, for example, preferred conditions are: concentration=35%; current density: l- A/dmP; electrolysis time=l5l80 sec. The conditions used for anodic oxidation may widely vary depending upon the type of treating solution, but the procedure used is conventional and well known to one skilled in the art.

The aluminum support processed in the present invention can be provided with a coating film of a light-sensitive material such as, for example, a mixture of a bichromate with polyvinyl alcohol, fish glue or egg albumin; a nitrogen-containing light-sensitive substance such as one containing a diazonium or tetrazonium compound; or a light- In accordance with the present invention, an aluminum support of uniform appearance free from unnecessary spoils and blackenings due to anodic oxidation can be obtained without deteriorating the merits of a support subjected to anodic oxidation. Therefore, the working efficiency in the various steps of plate making is markedly improved when using the aluminum support as a support for a printing plate. Furthermore, the elimination of the light-sensitive layer on a non-image area is as good as in the case of a plate not anodically oxidized, whereby developing is markedly raised.

The following non-limitative examples are given in order to illustrate the invention in greater detail.

Example 1 An aluminum-alloy plate (material quality: AA 3003) having a thickness of 0.3 mm. was washed with trichloroethylene to remove grease, grained by brushing with a nylon brush and an aqueous suspension of pumice powder (400 mesh) and to an Ha value of 0.40 and washed well with water. The plate was immersed in a 10% aqueous solution of sodium hydroxide at 30 C. for 30 seconds, washed with water, immersed in 20% nitric acid for 20 seconds and again washed with water. The etching rate of the grained surface reached a maximum of about 5.0 -g./m.

The etched plate was then subjected to anodic oxidation for 2 minutes at a current density of 1.6 A/dm. in an electrolytic bath of 15% aqueous sulfuric acid at a temperature of 27 0., followed by washing with water and drying.

For purposes of comparison, another plate was formed in the same manner but for omitting the etching treatment. The former plate had a plate reflection density D of 0.40- 0.43 while the latter plate had a D value of 0.700.80. The former was more excellent in appearance, uniformity and whiteness as compared to the latter. Both plates thus formed were suitable for use as a support for a printing plate on this point, each having a surface roughness of 0.45-0.48 micron by Ha indication.

Each plate was then coated with a mixture of a diazoxide resin and a phenol resin [5 parts by weight of the reaction product (prepared by reacting 62 g. of the condensation product of acetone and pyrogallol with 100 g. of Z-diazo-1-naphthol-S-sulfochloride) dissolved in parts of cyclohexane, prepared as described in British Pat. No. 1,113,759] and dried to provide a positive-positive type light-sensitive plate for plate printing.

The plate obtained in accordance with the present invention was in no way inferior to the prior art light-sensitive plate for printing with respect to the plate manufacturing operations of exposure to retouching and the printing operations, and had the advantage that discrimination of an image area was easy through the elevation in whiteness described above. vIn printing, it showed a durability (printing resistance) three times or more as great as an anodic oxidation-free printing plate. Generally, the whiteness of a plate suitable for printing is less than 0.5 in terms of reflection density. When a grained aluminum plate is subjected to anodic oxidation without etching treatment, the plate usually exhibits a reflection density in the range of from about 0.7 to about 1.0 which is not preferred for printing.

In accordance with the method of this invention which comprises first etching a grained aluminum surface with an etching solution then subjecting the etched surface to anodic oxidation, the reflection density of the resulting surface can generally be decreased to less than 0.5.

Example '2 The procedure of Example 1 was repeated except that a 12% aqueous solution of trisodium phosphate at 70 C. was used in place of the 10% aqueous solution of sodium hydroxide used in Example 1 as the etching bath.

The resulting aluminum support was excellent in appearance, uniformity and whiteness as in Example 1. A light-sensitive printing plate similar to that of Example 1 was prepared and subjected to plate making. The working efiiciency was excellent in plate making. The printing resistance of the plate was also good.

Example 3 The procedure of Example 1 was repeated except that the aluminum-alloy plate was subjected to a treatment in 30% sulfuric acid at 80 C. for 60 seconds in place of the treatment with sodium hydroxide and nitric acid and then s u bjected to anodic oxidation in the same bath at the conditions described in Example 1. Similar excellent results were obtained as in Example 1.

Example 4 After the procedures up to the anodic oxidation treatment as described in Example 1, the aluminum-alloy plate was treated with a 0.5% aqueous solution of potassium fluozirconate at 80 C. for 60 seconds, washed with watel and dried. This plate was coated with a condensate of di phenylamine-4-di-azonium and formaldehyde (1:1 molar ratio) to prepare a negative-positive type light-sensitive printing plate. The plate making and printing adaptability thereof were excellent, i.e., the fountain solution was easily controlled and the plate was easily handled in printing.

Example 5 An aluminum plate (material quality: AA 1001) 0.3 mm. thick was grained by the sandblasting method using 300 mesh sand and then subjected to etching treatment as in Example 1. The plate was then subjected to anodic oxidation by direct current electrolysis for 5 minutes at a current density of 2.0 A/dm. in a aqueous solution of oxalic acid as the electrolytic bath. Using this plate as a support, a printing plate similar to that of Example 1 was prepared, providing excellent results upon printing.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

What is claimed is:

1. A process of producing aluminum containing planographic printing plates, which comprises mechanically graining an aluminum surface, within the range of 0.5 to 30 g./m. etching the grained aluminum surface with a basic or acidic etching solution and then subjecting the etched surface to anodic oxidation.

2. The process of Claim 1 wherein the panographic printing plate is greater than 95% by wt. aluminum.

3. The process of Claim 1 wherein the planographic printing plate is aluminum.

4. The process of Claim 1 wherein the support is an aluminum alloy comprising greater than 95% aluminum and less than 5% by wt. of manganese, copper, zinc, titanium, iron, magnesium or chromium.

5. The process of Claim 1 wherein roughening is to an Ha value within the range of from about 0.2 to about 1.5,u.

6. The process of Claim 1 wherein the etching solution is basic and at a pH greater than about 11.

7. The process of Claim 1 wherein the etching solution is acidic and at a pH less than about 3.

8. The process of Claim 1 wherein anodic oxidation is in a bath comprising sulfuric acid.

9. The process of Claim 1 wherein the completed planographic printing plate has a reflection density less than 0.5.

10. The process of Claim 1 wherein the etching solution is basic and comprises a member selected from the group consisting of sodium hydroxide, potassium hydroxide, trisodium phosphate, disodium phosphate, tripotassium phosphate and dipotassium phosphate.

11. The process of Claim 1 wherein the etching solution is acidic and comprises a member selected from the group consisting of sulfuric acid, persulfuric acid and their salts.

12. The process of Claim 1 wherein etching is at a rate of aluminum dissolution of from about 0.3 to about g./m. per 1 minute of etching time.

13. The process of Claim 1 wherein anodic oxidation is in a bath comprising a member selected from the group consisting of sulfuric acid, oxalic acid, phosphoric acid or chromic acid.

14. The process of Claim 8 wherein anodic oxidation is at a current density of 1-15 A/dm. for 15-180 seconds using 1035 wt. percent sulfuric acid.

15. The process of Claim 1 wherein the etching and anodic oxidation are conducted in aqueous mediums.

16. An aluminum planographic printing plate produced by the process of Claim 1.

References Cited UNITED STATES PATENTS 3,594,289 7/1971 Watkinson et al. 20458 3,511,661 5/1970 Rauner et al. 204-58 3,330,743 7/1967 Jestl et al 204-58 3,031,387 4/1962 Deal et al. 204-58 2,708,655 5/ 1955 Turner 204-33 OTHER REFERENCES Cleaning & Etching Al by S. Spring, Metal Finishing, August 1968, pp. 66-71.

JOHN H. MACK, Primary Examiner R. L. ANDREWS, Assistant Examiner US. Cl. X.R. 20458 

